Antenna



R. E. CLAPP Aug. 9, 1949.

ANTENNA Filed Nov. 4, 1944 FIG-/ INVENTOR.

ROGER E. CLAPP FIG-J.

BY M 1%. LAM firm y Patented Au 9, 194@ R er B. Glenn. .Cam e; Ma sassi' mn. by

'esn a i rim ts, to thefiinitedf'states' of Ameri rep esen a th 'seeerer' War Application. ilove nberze, 194e, Se ia dotfifihttg:

4' C aims This. nv n n re ates. to an nnas. f r. Pr mieringnonsymrnetrical radiation patterns andfparticularly to antennas. forproducing patterns, wherein'the intensity of radiated energyvaries as,

a power function of cscti' (0. "being, the angle of radiation withrespect to the,hoi;iz'on In certainfecho detection systems, for.example, GCA (ground controlof approachin aircraft), apparatus, it isdesirable that the energy distribution in one plane throughout. arelatively wide angle follow a csc fl variation. Theoretically. thisprovides a radiation pattern. of such character. that the echo signalsreflected, for instance, from. an aircraft coming inat constantaltitudewill be as strong when the-targetis distantQsay, 30 miles, as. whenit isclose in, It. also enables the. simultaneous viewing of 116%.?- and,distant aircraft. in. search scanning. Conventional paraholiclreflecators do not satisfy these requirements, and more over it. is necessarytotilt the parabolic freflector. inorder to follow incoming aircraft. 2

In view of the foregoing, it is a salient object, of this invention toafford complete radiation coverage throughout a relatively wide angle inelevation and inconformity with; the desired mathematical relationbetween the intensity of radiatedenergy andan-gle of elevation. 2

A further object is to provide'a-novel and simple antenna FWQQHW: Q EH'i iQQi fiing ii para" bolic reflector and dipole elements so spaced as,toproduce a radiationpatternof csc e configura tion.

In this connection it should be noted;that, re cent investigation hasestablished the possibility that the exact type ofpattern desired may,be closer to a .csc configuration. The present invention has theadvantage that; it may be readily adapted to cover either case. 2

These and other novel features and advantages will be apparent from thefollowing disclosure.

In the drawings:

Fig. 1 is a partially diagrammatic View showing the manner in which theantenna may be mounted on a vehicle and the radiation pattern which itproduces;

Fig. 2 is a plan view of the antenna; and

Fig. 3 is an elevational view of the antenna; and Fig. 4 shows apreferred embodiment of my invention.

Referring to Figs. 2 and 3, the antenna consists of a dipole array whichis fed from a wave guide 1 and which directs its radiated energy againsta cylindrical parabolic reflector 5. The spacing and number of thedipole elements 6 along the Wave guide I, in addition to the phasing andenergization of eacheiementand co unction withthe, shape, of; thereflector fi; determine the: shape of the intensity pattern in averticalplane: The. dipoles are mounted" on one face of the glljdel andareenergizedfin a known manner by probe extendin in tne id rte-primar es:

parabol c. refl tor. 5? .c n en rates' th d ated" energy into, a rathernarrow beam in the. horizontal plane. The effective linesourceof radiaonof thedigole ra s le ei near-t f a line of the parabolic lcylinder jthatis, approximately to the nearest halfiwaveleng th'in air;

Fig. 1 illustrates the device. as" mounted in a mobiletypeofsearchstation. The antennamay I, be used; in this instance to produce aPEI(plan pes uo inaiceton: typ offswh b th 'sw' rounding vicinity is sweptperiodically with the; beam from the antenna; The primary function ofsuch a device; is to search. for and'detect the existence of aircraftthe vicinity, and" as such, the pattern desired should varyapproxirnately as. 050%. That is, an. airplane, flying infrom a d s c aa on n t tude i wa ih tion shouldbesubjected to: an drefiect a varyi g;m n en rg to du estent' r ga n d signalsa th sta n r a dle s e ih ma mation of the aircraft." 2

T nt rin ir eie in' a imu by mean which will be described; presently:It-is' apparent that the resolution in azimuth: of the system:de=

pendsupon the beam-width-oftlie ra-diationpat tern. Preferably thehorizontal beamwidthshould be approximately constant for a-ll values of'B-to provide l uniform resolution over the field? I The cylindricalparabolafiiprovidesa satisfactory solution to this problem.

To obtain the proper energy distribution inthe vertical plane, thespacing 'of 'the dipoles' 6 may be approximatelyas-fol-lows% Qver thelengtl'i A' (Fig. 3) representing approximately two-thirds the length ofthe array, the dipoles 6 are spaced apart slightly less than a halfwavelength. Starting from point P and along the length B, the dipoles Bare spaced gradually closer together so that at the upper end of thearray the spacing is approximately two fifths of a wavelength. Thisparticular spacing has given satisfactory results, although the patternmay be modified if desired by varying the spacing. If, for example, itis determined that the desired radiation pattern is closer to csc 0rather than csc e, such variation can be achieved by spacing the dipoles6 accordingly. It should also be noted that in practice the beam patternis so adjusted that the peak is elevated slightly above the horizon, asindicated by the line Z in Fig. 1, and the beam-cuts off sharply belowthis line so as to minimize ground interference.

In general, when the dipole spacing is varied, three factors areaffected: (1) the sharpness of the beam pattern below the line Z, Fig. 1is changed; (2) the side lobes are changed; and (3) the verticalcoverage of the beam is modified. When the vertical coverage isimproved, that is, the curvature of the beam pattern over region X (seeFig. 1) is increased, the sharpness of the beam pattern below the line Zis diminished. Depending upon the relative importance of these factors,the beam may be adjusted to the desired shape. The shape is alsogoverned by the amount of energy radiated from each element 6, which maybe adjusted by the depth to which their respective pick-up probes extendinto the wave guide 1, Figs. 2 and 3. r

The reflector 5 and the waveguide I feedin the dipoles 6 are supportedVertically in fixed relation to each other on a rotating table 8provided with gear teeth [2, Figs. 2 and 3. The waveguide 1 is, in thisinstance, at the center of the table 8, and is coupled through arotatable joint 9 to the transmitting and receiving means (not shown). Aportion of the table 8 is broken away as indicated at Y to more clearlyshow the waveguide joint. A pinion Ill meshing with the gear 8 ismounted on the shaft of a motor II which drives the antenna structurewhen search scan ning is being performed.

The nature of the antenna structure may be such as to require thatenergy be fed to the top of the dipole array in order that the desiredenergy distribution will be developed in space. Fig. 4 illustrates thisstructure. Radio frequency energy is coupled through rotatable joint 9to waveguide I3 which conducts the energy upwardly to bended section l4.Section [4 routes the energy to the top of waveguide 1 which directs theenergy downwardly to the radiating dipoles 6. Moreover, it will beappreciated that the dipole array need not be at the center of rotationso long as the desired spacing between the dipoles and the reflector ismaintained.

While I have illustrated and described a selected" embodiment of myinvention, it is apparent that variations and modifications may be madeby those skilled in the art, and therefore I do not desire to limit thescope of the invention to the precise details disclosed herein but wishto avail myself of all improvements and modifications within the purviewof the following claims.

-I claim:

1. A combined transmitting and receiving antenna for use in radioobject-locating apparatus,

4 comprising a cylindrical parabolic reflector and an array of radiatingelements positioned on the focal line of said reflector, said elementsbeing spaced closer together at one end of said array than at the otherend thereof and means for controlling the amount of energy radiated fromeach of said elements to produce a radiation'pattern resulting insubstantially uniform received signals at said antenna irrespective ofthe radiation angle of reflecting objects disposed along a substantiallyhorizontal path in the plane of said reflector and radiating elements.

2. Anantenna for use in radio object-location I comprising avertically-extending cylindrical parabolic reflector and an array ofdipole elements arranged along the focal line of said reflector, saiddipole elements being spaced apart.

by substantially a half Wavelength for approximately the lowertwo-thirds of the length of.

the array, and being spaced gradually closer together for the upperone-third of the length of the array so as to attain a spacing ofsubstantially two-fifths of a wavelength at the upperend thereof.

3. An antenna as claimed in claim 1, wherein. said elements are spacedprogressively closer together at one end of said array than at the otherend thereof.

4. An antenna for use in radio object-location. comprising avertically-extending cylindrical parabolic reflector and an array ofdipole elements arranged along the focal line of said refiector, saiddipole elements being spaced apart by substantially a half wavelengthfor approximately the lower two-thirds of the length of the array, andbeing spaced gradually closer together for the upper one-third of thelength of the array so as to attain a spacing of substantiallytwo-fifths of a wavelength at the upper end thereof, and means forrotating said reflector and said array in fixed relation to each other.

ROGER E. CLAPP.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,908,595 Franklin et a1 May 9,1933 2,156,653 Ilberg May 2, 1939 2,275,646 Peterson Mar. 10, 19422,276,497 Kroger Mar. 17, 1942 2,408,435 Mason Oct. 1, 1946 2,427,688Norgaard Sept. 23, 1947 2,436,380 Cutler Feb. 24, 1948 2,438,735Alexanderson Mar. 30, 1948

